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Java example source code file (AddressResolverGroup.java)

This example Java source code file (AddressResolverGroup.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

addressresolver, addressresolvergroup, closeable, eventexecutor, exception, futurelistener, identityhashmap, illegalstateexception, internallogger, net, network, nullpointerexception, override, suppresswarnings, suspicioustoarraycall, threading, threads, throwable, util

The AddressResolverGroup.java Java example source code

/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package io.netty.resolver;

import io.netty.util.concurrent.EventExecutor;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.FutureListener;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

import java.io.Closeable;
import java.net.SocketAddress;
import java.util.IdentityHashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentMap;

/**
 * Creates and manages {@link NameResolver}s so that each {@link EventExecutor} has its own resolver instance.
 */
public abstract class AddressResolverGroup<T extends SocketAddress> implements Closeable {

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(AddressResolverGroup.class);

    /**
     * Note that we do not use a {@link ConcurrentMap} here because it is usually expensive to instantiate a resolver.
     */
    private final Map<EventExecutor, AddressResolver resolvers =
            new IdentityHashMap<EventExecutor, AddressResolver();

    protected AddressResolverGroup() { }

    /**
     * Returns the {@link AddressResolver} associated with the specified {@link EventExecutor}. If there's no associated
     * resolved found, this method creates and returns a new resolver instance created by
     * {@link #newResolver(EventExecutor)} so that the new resolver is reused on another
     * {@link #getResolver(EventExecutor)} call with the same {@link EventExecutor}.
     */
    public AddressResolver<T> getResolver(final EventExecutor executor) {
        if (executor == null) {
            throw new NullPointerException("executor");
        }

        if (executor.isShuttingDown()) {
            throw new IllegalStateException("executor not accepting a task");
        }

        AddressResolver<T> r;
        synchronized (resolvers) {
            r = resolvers.get(executor);
            if (r == null) {
                final AddressResolver<T> newResolver;
                try {
                    newResolver = newResolver(executor);
                } catch (Exception e) {
                    throw new IllegalStateException("failed to create a new resolver", e);
                }

                resolvers.put(executor, newResolver);
                executor.terminationFuture().addListener(new FutureListener<Object>() {
                    @Override
                    public void operationComplete(Future<Object> future) throws Exception {
                        synchronized (resolvers) {
                            resolvers.remove(executor);
                        }
                        newResolver.close();
                    }
                });

                r = newResolver;
            }
        }

        return r;
    }

    /**
     * Invoked by {@link #getResolver(EventExecutor)} to create a new {@link AddressResolver}.
     */
    protected abstract AddressResolver<T> newResolver(EventExecutor executor) throws Exception;

    /**
     * Closes all {@link NameResolver}s created by this group.
     */
    @Override
    @SuppressWarnings({ "unchecked", "SuspiciousToArrayCall" })
    public void close() {
        final AddressResolver<T>[] rArray;
        synchronized (resolvers) {
            rArray = (AddressResolver<T>[]) resolvers.values().toArray(new AddressResolver[resolvers.size()]);
            resolvers.clear();
        }

        for (AddressResolver<T> r: rArray) {
            try {
                r.close();
            } catch (Throwable t) {
                logger.warn("Failed to close a resolver:", t);
            }
        }
    }
}

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